Many natural and synthetic materials are known to be useful as lubricants, their utility in particular applications depending on factors such as their stability and viscosity under the conditions of use, their pour points, and their compatibility with any materials with which they will be used. Among these known materials are ester oils, such as alkyl alkanoates, alkyl diesters of aliphatic and aromatic dicarboxylic acids, and fatty acid esters of neopolyols.
In refrigeration applications (e.g., home-use or industrial-use refrigerators, freezers, or air conditioners for buildings, automobiles, airplanes, and other vehicles), the need to replace chlorofluorocarbon refrigerants with a refrigerant having lesser ozone-depleting potential has made it important to find lubricants which would be suitable for use with fluorohydrocarbons--especially 1,1,1,2-tetrafluoroethane (R-134a), a refrigerant that has been reported to have an ozone depletion potential of zero. Mineral oils, usually the refrigeration lubricants of choice in the past, cannot be utilized in this application because of incompatibility with such refrigerants.
It would be desirable to be able to employ the aforementioned ester oils as lubricants in refrigeration compositions containing fluorohydrocarbons. However, a criterion for lubricants in such compositions is complete miscibility with R-134a over the entire temperature range to which the compositions are apt to be exposed in refrigeration equipment (generally temperatures in the range of about -40.degree. C. to 70.degree. C.), and many of these ester oils lack that miscibility--at least when used in an amount such as to provide the fluorohydrocarbon/ester oil weight ratio at which it is usually believed to be most important for complete miscibility to be achieved, i.e. 4/1.
Copending applications Ser. No. 07/947,628 (Sabahi) and Ser. No. 07/986,204 (Sabahi et al.) teach ester oils which have excellent miscibility with refrigerants, including R-134a and other fluorohydrocarbons, and are useful as lubricants in refrigeration compositions containing them. These novel lubricants are oils composed of molecules corresponding to the formula ROOC--CH.sub.2 CH.sub.2 --[(ROOC)CHCH.sub.2 ].sub.m --C(COOR).sub.2 --[CH.sub.2 CH--(COOR)].sub.n --CH.sub.2 CH.sub.2 COOR in which the R's represent alkyl groups of 1-30 carbons, at least 10% of which are alkyl groups of 1-4 carbons, and each of m and n represents zero or a positive integer such that the sum of m and n in a molecule is 0-30, preferably 0-10.